This invention relates to faulted current indicators, and particularly to methods and means for displaying a faulted current condition while ignoring high inrush currents.
Faulted current indicators (or FCI's or fault indicators) are placed at intervals along power lines to disclose that a fault has occurred between the indicator and a load. In general, each FCI trips in response to an overcurrent that occurs as a result of a fault between the indicator and the load. The FCI remains in the trip indicating condition even after a current protection device, such as a circuit breaker or a fuse, in the line has responded to the overcurrent by opening the line and ending the current in the line. After the fault has been cured and the current protection device closed to re-energize the line, the FCI resets in response to a minimum operating current. Such devices often respond unintentionally to energization inrush currents and therefore frequently provide inaccurate information.
Attempts to have FCI's disregard inrush currents have had limited success because they required extended outages for operation and were unable to ignore long term inrushes. The devices described in the aforementioned application overcome such disadvantages by disabling the trip operation in response to inrush currents that occur immediately upon energization. However, such devices depend upon a minimum operating current to initiate the inrush restraint. If the minimum current does not occur until after the inrush current time has passed, the FCI may mistake an actual fault overcurrent for an inrush current and thereby fail to trip.